A very significant proportion of lumber and construction panels are currently shipped and stored in bundles or piles wrapped in a waterproof envelope in order to provide a protection against alterations due to weather conditions and stabilise the humidity level.
Traditionally, the placement and folding of the wrapper sheet has mostly been carried-out in a semi-automatic fashion, a web like material being supplied from a material roll positioned above the article to be wrapped. Also, prefabricated plastic envelopes (bags) are currently used to speed-up the wrapping operation. The bag is generally installed from the top of the bundle, thus protecting the top and the sides of the bundle, while allowing some air circulation through the bottom. In this latter case, the envelope is manually secured to the bundle by stapling into the wood pieces. In this case, the operation is still quite expensive since extensive manpower is still required and the cost of the envelopes is relatively high.
Many automated solutions have been proposed in the prior art to wrap pelletised articles in a plastic film or web. However, most of these solutions perform the wrapping operation by rotating a narrow plastic film roll around the load on a spiral path. Such techniques are not practical for elongate articles such as lumber bundles and do not provide automatic installation of a top web member nor yield a neat result.
It is also known in the art to use an automated system to slide a bundle of lumber into a bag that is then manually closed and sealed at one end. The economic performance of that process is still limited since expensive large prefabricated bags are required in a wide range of sizes, thus also resulting in inventory concerns.
Also known in the art, there is the U.S. Pat. No. 5,657,608 which discloses a fully automated method for wrapping a parallelpipedly shaped article such as a bundle of lumber, using a web like material supplied from a roll located over the article. The wrapper material is dispensed and folded around the article in a continuous process by the relative movements of a backing means and the article, plus the movement of the article with respect to spring loaded rollers as folding members. The principal embodiments of that invention as described show several limitations and drawbacks. The main drawback is certainly the fact that the process must be continuously, so that a new set-up is required after each time an incoming article does not require wrapping, that situation occurring frequently since only a part of lumber shipments must be wrapped. It shall also be noted that the folding caused by the rollers is not precisely controlled and will generally yield a poor looking result and very visible folding lines on the long sides of the article. That poor looking result is also subject to be emphasised by the presence of static electricity in plastic based wrapper material. Moreover, it is worth indicating that it is generally not acceptable to apply adhesive all over the article to hold the web in place. Another obvious limitation of that process is that the article is moved back and forth a few times to complete the wrapping. Since the contemplated articles are long and heavy, a lot of time and energy is required.